title: Enhanced autophagy blocks angiogenesis via degradation of gastrin-releasing peptide in neuroblastoma cells.
abstract: Neuroblastoma is characterized by florid vascularization leading to rapid tumor dissemination to distant organs; angiogenesis contributes to tumor progression and poor clinical outcomes. We have previously demonstrated an increased expression of gastrin-releasing peptide (GRP) and its receptor, GRPR, in neuroblastoma and that GRP activates the PI3K-AKT pathway as a proangiogenic factor during tumor progression. Interestingly, AKT activation phosphorylates MTOR, a critical negative regulator of autophagy, a cellular process involved in the degradation of key proteins. We hypothesize that inhibition of GRPR enhances autophagy-mediated degradation of GRP and subsequent inhibition of angiogenesis in neuroblastoma. Here, we demonstrated a novel phenomenon where targeting GRPR using shRNA or a specific antagonist, RC-3095, decreased GRP secretion by neuroblastoma cells and tubule formation by endothelial cells in vitro. Furthermore, shGRPR or RC-3095 treatment enhanced expression of proautophagic proteins in human neuroblastoma cell lines, BE(2)-C, and BE(2)-M17. Interestingly, rapamycin, an inhibitor of MTOR, enhanced the expression of the autophagosomal marker LC3-II and GRP was localized within LC3-II-marked autophagosomes in vitro as well as in vivo, indicating autophagy-mediated degradation of GRP. Moreover, overexpression of ATG5 or BECN1 attenuated GRP secretion and tubule formation, whereas opposite effects were observed with siRNA silencing of ATG5 and BECN1. Our data supported the role of autophagy in the degradation of GRP and subsequent inhibition of angiogenesis. Therefore, activation of autophagy may lead to novel antivascular therapeutic strategies in the treatment of highly vascular neuroblastomas.
authors.affiliation: Department of Pediatric Surgery; Vanderbilt University Medical Center; Nashville, TN USA.
authors.forename: Kwang Woon
authors.initials: KW
authors.lastname: Kim
authors.affiliation: Department of Pediatric Surgery; Vanderbilt University Medical Center; Nashville, TN USA; Department of Cancer Biology; Vanderbilt University Medical Center; Nashville, TN USA.
authors.forename: Pritha
authors.initials: P
authors.lastname: Paul
authors.affiliation: Department of Pediatric Surgery; Vanderbilt University Medical Center; Nashville, TN USA.
authors.forename: Jingbo
authors.initials: J
authors.lastname: Qiao
authors.affiliation: Department of Pediatric Surgery; Vanderbilt University Medical Center; Nashville, TN USA.
authors.forename: Sora
authors.initials: S
authors.lastname: Lee
authors.affiliation: Department of Pediatric Surgery; Vanderbilt University Medical Center; Nashville, TN USA; Department of Cancer Biology; Vanderbilt University Medical Center; Nashville, TN USA.
authors.forename: Dai H
authors.initials: DH
authors.lastname: Chung
mesh_terms: D001343:Autophagy / Q000235:genetics / Q000502:physiology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000502:physiology; D042783:Endothelial Cells / Q000378:metabolism; D019886:Gastrin-Releasing Peptide / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D009389:Neovascularization, Pathologic / Q000235:genetics / Q000378:metabolism*; D009447:Neuroblastoma / Q000098:blood supply / Q000378:metabolism* / Q000473:pathology; D059748:Proteolysis; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism
chemical_list: D034741:RNA, Small Interfering; D019886:Gastrin-Releasing Peptide; D051057:Proto-Oncogene Proteins c-akt
keywords: GRP; angiogenesis; autophagy; endothelial cells; neuroblastoma; rapamycin